If your in the summer season and go down the stairs by the tree root dungeon an old man talks about killing 4 golden beast to get some power. I've killed three so far. One by the shore next to the hero's cave, one in front of the snake dungeon, and one in spool swamp. Does anyone know where the fourth one is? This is really driving me crazy 'cause I really want the freakin' power! Also does anyone know what the power is?

There are no Golden Beasts in The Legend of Zelda: Oracle of Ages, you must be talking about The Legend of Zelda: Oracle of Seasons.

Anyway, I think this is the Golden Beast you are taking about:

Golden Lynel - WinterIn the Tarm Ruins Change the Season to Winter via tree stump near the small pool of water with Armos Statues. Then head right (you must have the Armos Statues already moved) to find the Golden Lynel.